CFD investigation on combustion and NOx emission characteristics in a 600 MW wall-fired boiler under high temperature and strong reducing atmosphere

Abstract

In this paper, a modified air staging technology for pulverized coal boilers was proposed, to notably reduce NOx emission by creating a zone with high temperature and strong reducing atmosphere (HT&SRA) in furnace. Here, the conventional air staging technology was employed in combination with increasing O2 fraction of feeding gas in primary zone (O2.p). The new technology was numerically verified in a 600MW wall-fired boiler and the temperature distribution, the char burnout and the effectiveness in NOx reduction were mainly examined. The results indicate that a sufficiently low stoichiometric O2 ratio in primary zone (SRp) is essential to reduce NOx emission by increasing O2.p. The effectiveness in NOx reduction by increasing O2.p also depends greatly on the injection position of over fire air (OFA). Under the condition of 0.7 SRp and a relatively high OFA position, the NOx emission could be reduced by 27.6% when O2.p is increased from 21% to 33%, while the incomplete combustion heat loss only shows a slight rise. In addition, the NOx reduction ratio could reach to >60% through the proposed low-NOx combustion technology compared with the current operation condition.